In typical thermal printers, a resistive element thermal head is used to transfer dye from a dye bearing donor web to a dye receiving member. The head, dye donor and receiver are brought into contact, and the thermal head elements are selectively energized to transfer variable quantities of thermal dye from the donor to the receiver. The receiver is advanced past the thermal head in a controlled manner so that sequential lines of pixels are generated until a complete image is formed on the dye receiver. The transferred dye remains close to the surface of the receiver and is susceptible to mechanical, chemical and thermal aging and deterioration. Increased printing speed is always desirable, but as a result, the dye image becomes even more susceptible to damage. In addition, mechanical deformation occurs in the print as speed increases and the quantity of dye increases.
Image stability can be improved by applying post printing heat to fuse the image. This can be done by passing the image between two heated rollers as is done in electrophotographic printers. In electrophotographic printers, the heat is provided by passing a lamp inside a rotating cylinder. Having the lamp inside allows full heat transfer to the roller while allowing the roller to rotate freely. However, a disadvantage of this system is that the mechanism must be completely disassembled when the heating element or roller has to be serviced.
In some printing processes, the dyes are reheated by rollers that apply a controlled amount of heat to the image bearing surface. Heater elements do not last forever and must be serviced and eventually replaced. Unfortunately, heater elements and fuser bars are not easily accessible. U.S. Pat. No. 4,896,166 discloses a replaceable thermal head that can be inserted and removed without tools. A difficulty with the replaceable thermal head is that it is an electrical device and requires electrical cabling to the printer. Accordingly, it will be appreciated that it would be highly desirable to have a fusing apparatus that provides even, constant temperature heat for fusing and that is easy to install and remove without tools.